1. Field of the Invention
The present invention relates to a magnetic recording medium such as a magnetic tape, a magnetic disc and a magnetic card. More particularly, it relates to a magnetic recording medium comprising a lubricant on a surface of a magnetic layer.
2. Description of the Prior Art
A magnetic recording medium comprising a substrate and a magnetic layer which is formed on the substrate and consists of a thin film of a metal or a metal oxide with high coercive force has an extremely smooth surface and a large coefficient of friction, so that it is easily abraded or damaged when it contacts a magnetic head and/or a guide during recording or reproducing. To prevent abrasion and damage of such a magnetic layer, it has been proposed to coat the surface of the magnetic layer with a lubricating layer comprising higher fatty acids or their metal salts, and macromolecular compounds such as organic silicon compounds, whereby the coefficient of the surface of the magnetic layer is reduced so as to improve abrasion resistance, durability and running stability of the magnetic recording medium.
For a magnetic recording medium comprising a magnetic coating layer formed by applying a magnetic paint and drying it, improvement of abrasion resistance of the magnetic layer is increasingly required with the increase of surface smoothness of the magnetic layer which is desired for better electromagnetic conversion characteristics. To this end, it has been proposed to coat the surface of the magnetic layer with various lubricants to form a protective film with good lubrication, or to add the lubricant to the magnetic coating layer so as to exude it on to the surface of the magnetic layer.
When the surfaces of the magnetic layer and of the magnetic head or the tape guide are extremely smooth, under a circumstance when the magnetic recording medium contacts the magnetic head at a high speed, the lubricant cannot exert sufficient lubrication effect and viscosity resistance of the lubricant increases so that the running stability of the medium deteriorates and, in turn, fluctuation of the output is increased. Furthermore, the magnetic recording medium sticks to the tape guide and running of the medium is stopped.